The invention relates to an image pickup device. Attempts are increasingly being made to reduce the bulk of photographing devices. This need is particularly great, for example, when wishing to integrate such a device in a mobile telephone in order to add a video recorder or photographic function to the telephone function.
To this end, photographing devices are produced which comprise a sensor produced on an electronic component, on top of which there are optical means. For example, such a photographing device has a horizontal object field of 50° and a matricial sensor comprising 640 points per row and 480 points per column, which is well known by the name VGA (video graphics array) sensor. The optical means then need to have a minimum focal length of 3.8 mm. Using only a converging lens to produce the optical means, it is impossible to reduce the height of the optical means as measured along the optical axis of the lens to less than the focal length, i.e. 3.8 mm. In practice, such optical means have a height of not less than 6 mm. This is because the thickness of the lens tends to lengthen the optical path. In order to reduce the thickness of the optical means, a diverging lens may be arranged between the converging lens and the sensor. In practice, such an embodiment does not make it possible to reduce the thickness of the optical means to less than 5 mm.
Furthermore, a photographing device in the VGA format having a horizontal object field of 50° in reality has a total object field of 66° as measured along the diagonal of the sensor. This wide field leads to aberrations which are commensurately greater as the aperture is large. Lenses whose surfaces are aspherical are used in order to correct the field aberrations. However, the use of this type of lens imposes tight positioning tolerances of the lens between one another and with respect to the sensor. For example, for a photographing device whose total object field is 66° and whose maximum aperture is 2.8, the positioning precision of the lenses must be less than 15 μm. Such a precision is extremely difficult to obtain when wishing to mass produce the photographing device at a small production cost.